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Within a subtle exterior, the £135 million extension exemplifies the practice’s skill in designing for users, writes Laura Mark. Photography and film by Jim Stephenson

Rogers Stirk Harbour + Partners is no stranger to the Stirling Prize. The firm has been shortlisted seven times and won the award twice, for its terminal at Barajas Airport in Madrid and its west London Maggie’s Centre. However, it probably came as a surprise to some that the practice’s World Conservation and Exhibitions Centre (WCEC) at the British Museum appeared on this year’s shortlist, three years after it opened to the public. ‘We like to wait until a building is really completed until we put it in for awards,’ says project architect John McElgunn. ‘That means it has to also be occupied and in use. They are still moving objects into here and they probably will be for the next decade but it was the last year we could enter.’

The building is animated with people and exemplifies the practice’s skill in designing for users. But leaving it this long to enter carries its risks. There were teething problems with the lifts, many of the staff who worked in the museum’s old facilities have now moved on and, as with any glass building, there are elements that could do with a good clean.

What the Stirling Prize judges will also have seen at the £135 million WCEC, though, is the huge achievement of getting a building of this size and scale constructed, and the transformation it has brought to the historic institution. The project, which is one of the largest in the British Museum’s 260-year history, provides it with a new major exhibition gallery, laboratories, studios and storage. It seems simple, but for an institution that had previously had to load all its artworks up the front steps while the museum was closed, it is a major change.

Previously, the museum’s collection of ancient objects had been stored on three different sites across London. The 5,100m2 of storage at the new building allows more of its collection to be brought back to the Bloomsbury site, where the environmentally controlled facilities allow items to be stored, seen and studied. The studios and research laboratories on the upper floors of the building are naturally lit and open. They are flexible spaces which can be reconfigured to accommodate larger historic pieces. Here, one of the museum’s staff could be working on an ancient canoe while another is working on a tiny brooch.

Its overseas loans programme, which ships more than 5,000 objects from the collection to more than 300 institutions, galleries, and museums around the world each year, can also now be overseen from the Bloomsbury site. A new 42-tonne truck lift, which I’m told is the biggest in Europe, helps to ferry the historic objects to and fro from the storage. A road, like a secret highway for artworks, also runs through the new extension’s ground-floor level connecting the delivery area and storage spaces with the new exhibition hall and out to the roads beyond.

Until this building’s completion, the museum’s temporary exhibition space was in what had previously been the reading room. Designed by Sydney Smirke and opened in 1857, the reading room held books from the British Library until it moved out to its new site at St Pancras. The Grade I-listed structure, with its round walls, was not suitable for large exhibitions nor the British Museum’s increasing visitor numbers, so with the WCEC came a new purpose-built exhibition space: the Sainsbury Exhibitions Gallery.

Tucked away at the far side of Foster + Partners’ Great Court, the gallery is basically a 1,100m2 black box. It is capable of operating independently of the rest of the museum with potential for 24/7 public access and has its own foyer and shop. The space, like much of that in the WCEC, can be reconfigured depending on the exhibition, with moveable walls, tracks for partitions and services, and ceiling heights in excess of 6m. When it opened in March 2014, it showed off this new ability to display large works with the installation of a 37m-long reconstruction of a Viking warship.

While what goes on inside the building is highly technical, the outside gives the appearance of being less so – more a subtle, calm and simple composition which adds a modern take on the Bloomsbury aesthetic. Bordered by seven listed buildings, the museum’s extension is surrounded by Georgian terraces and larger Portland Stone institutional buildings. It was never going to be easy to get a new, modern building through in this highly contentious neighbourhood where many would have rather seen a mock-Georgian 70s terrace retained than the RSHP scheme.

In 2009, Camden Council said no to the original proposal for the building, raising concerns about the scheme’s massing and site coverage. RSHP had to go back to the drawing board, returning with the solution of placing one of the five pavilions which make up the building below ground. ‘It showed the strength of the design that we could do that,’ remarks McElgunn.

The height of the pavilions creates a subtle transition from the grand scale of the museum to the domestic proportions of the surrounding streets. The building’s stone façade and kiln-formed glass are inspired by the surroundings, yet add a contemporary twist. RSHP was keen that the Portland stone, here a shell fragment-saturated Roach stone, did not deceive and should appear loadbearing, as it does on the bordering part of the British Museum. Nevertheless the stone never touches the ground, instead sailing above it and finishing just short, supported by a beautifully engineered steel frame.

The WCEC is similar to a highly engineered data centre. It plugs into the back of the British Museum like a life support machine or battery back-up pack. As the museum changes over time, again adapting to new technologies, the building has the capacity to do so too. This is long-life, loose-fit in the truest of forms.

Laura Mark is architecture projects manager at the Royal Academy

How we built it

The development needed to provide a series of flexible spaces to support the wide range of activities undertaken by the British Museum. The design approach was driven by the nature of the site: four linked pavilions are arranged to respect the existing façades of the King Edward VII building and Smirke building and allow daylight to penetrate existing spaces. The mass of the development is on the east of the site, creating good connectivity with the existing museum and mitigating the impact on the Bedford Square properties.

Functional requirements are arranged vertically across the pavilions. The Collections Storage Facility is located below ground where the heavy floor loading can easily be accommodated and where the most stable environmental conditions can be provided. Above this sits the new logistics hub. The Special Exhibitions Gallery is at Level 2 (main gallery level in the museum) alongside the Great Court, providing the best connectivity and enhancing visitor experiences. The conservation studios are at the top, providing good-quality daylight and enabling fume extraction and ventilation to be placed at the top of the building. A green roof encourages biodiversity.

The scheme is arranged in two main elements: primary ‘served’ spaces such as offices and laboratories in the main buildings; and an adjacent services and circulation core serving each pavilion. This allows maximum flexibility of space within the pavilions and an efficient use of the cores, generating a clear logic of movement and use.

Despite being one of the largest redevelopment projects in the museum’s history, construction proceeded without a single gallery being closed to the public. The outer perimeter of the WCEC’s basement was constructed using 480 contiguous secant piles. These piles form the basement’s primary structural perimeter and enabled excavation down to 19m below street level.

Dwgs stp2017 british museum wcec by rsh+p3

Within the perimeter, a concrete frame was used to construct the five basement storeys. These contain the museum’s collection storage facility, its science facility, and the logistics level. The concrete creates a beautiful and robust space that, through its high thermal mass, can help moderate any minor fluctuations in environmental conditions. The radiotherapy room required further stability and was given a 6-tonne lead door and 900mm-thick walls.

Above ground, the steel frame was manufactured off-site to ensure high build quality and reduce construction time – the building rose from street to roof level in three months. The building’s exterior is clad in more than 1,600 hand-finished, kiln-formed glass planks, which allow a veil of privacy between the street and the private functions of the museum, but allow daylight in. The glass, etched with contour patterns inspired by Devon’s Jurassic Coast, has a matte, translucent quality that gives a sense of solidity from the outside. This effect complements the Portland Roach stone, also from the Jurassic Coast, used to clad the stair towers.

A vast truck lift was installed in the north-west corner of the site to ensure that large and fragile objects can be handled quickly and safely. Within minutes of arriving on site, a 42-tonne vehicle can be manoeuvred down to the logistics level in safe and secure conditions.

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